Strange data while importing DEM and Contour files into blender via Blender GIS - addon
I just have the same problem yesterday, if you want to fix it, you need to change the right coordinate (CRS) in QGIS or ArcGIS first. For reference coordinate you can find it in google as free, because each area or zone has different coordinate.
Then, after do that, when you try to import .shp in BlenderGIS you can see in the bottom right corner in Blender after import it, change elevation so from geometry to Field and select elev field same as contour table in your open atribute table in you GIS software. OK.
Or if you want the easier way, you can try to create contour from your DEM data to ArcGIS first:

Import DEM.TIF to ArcGIS
Create Contour from DEM.TIF
Create TIN from Contour, coordinate use Web Mecrator
Create TIN_LINE from TIN
Import TIN_LINE.shp to Blender



In Blender -&gt; Click ur Contour -&gt; GIS -&gt; Mesh -&gt; Delaunay